Large aperture deployable reflectarray antenna

ABSTRACT

A deployable reflectarray has a plurality of strips arranged in quadrants forming the reflectarray. The copper ground plane and the copper dipoles are supported by facesheets made of epoxy reinforced by quartz fibers. The copper ground plane is separated from the copper dipoles by S-shaped springs made of epoxy reinforced by quartz fibers, which allow folding and deployment of the reflectarray.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 62/687,373, filed on Jun. 20, 2018, and U.S. ProvisionalPatent Application No. 62/821,784, filed on Mar. 21, 2019, thedisclosures of both being incorporated herein by reference in theirentirety.

STATEMENT OF INTEREST

The invention described herein was made in the performance of work undera NASA contract NNN12AA01C, and is subject to the provisions of PublicLaw 96-517 (35 USC 202) in which the Contractor has elected to retaintitle.

TECHNICAL FIELD

The present disclosure relates to antennas. More particularly, itrelates to a large aperture deployable reflectarray antenna.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent disclosure and, together with the description of exampleembodiments, serve to explain the principles and implementations of thedisclosure.

FIGS. 1-2 illustrate an overview of the Large-Area DeployableReflectarray (LADeR).

FIG. 3 illustrates strips forming the reflectarray.

FIG. 4 illustrates wrapping of the strips.

FIG. 5 illustrates a predicted wrapped cross-section of thereflectarray.

FIG. 6 illustrates a cross-section of the molds used to fabricate astrip substrate.

FIG. 7 shows the measured RF gain.

FIG. 8 illustrates the azimuth for the antenna beam pattern.

FIG. 9 illustrates the elevation for the antenna beam pattern.

FIGS. 10-11 illustrate packaging of the reflectarray.

FIG. 12 illustrates surface flatness measurements for the reflectarray.

SUMMARY

In a first aspect of the disclosure, a method is described, the methodcomprising: deployable reflectarray antenna comprising: a plurality ofdeployable booms; a radio frequency feed; and a reflectarray supportedby the plurality of deployable booms and configured to: be stored in afolded configuration within a satellite bus, and deploy out of thesatellite bus into a deployed configuration during operation of thesatellite, the reflectarray comprising: a plurality of strips, eachstrip of the plurality of strips comprising: a conductive ground plane;a first facesheet attached to the conductive ground plane; a secondfacesheet; a plurality of conductive dipoles attached to the secondfacesheet; a plurality of collapsible S-shaped springs attached to thefirst facesheet and to the second facesheet, and being configured to:collapse during folding of the reflectarray, thus allowing adjacentfacesheet to fold against each other in the folded configuration, andprovide mechanical support for the reflectarray in the deployedconfiguration, separating adjacent facesheet; and a plurality ofligaments joining adjacent strips of the plurality of strips.

DETAILED DESCRIPTION

The present disclosure describes large-area deployable reflectarrayantennas for CubeSats applications. In particular, the presentdisclosure describes, as an exemplary embodiment, a 1.5 m×1.5 mreflectarray antenna designed to stow in a cylinder with a diameter of20 cm and a 9 cm height, and then be unfolded to provide an aperturesuitable for radio frequency (RF) operations at the X-band (e.g. 8.4GHz) while producing 39.6 dB of gain or better. In the following,parameters for the exemplary embodiment will be described; however, theperson of ordinary skill in the art will understand that in otherembodiments some of these parameters may be different. The mass of thereflectarray can be, for example, 1.75 kg. The reflectarray can comprisea number of crossed-dipoles held 5 mm above a ground plane. While insome embodiments the dipole elements are symmetrical crosses, in otherembodiments the elements may be asymmetrical crosses with unequallengths in the perpendicular arms, which allow independent scans orshaping of the horizontal and vertical polarization patterns. In yetother embodiments, elements may have other shapes, such as, for example,rings, loops, concentric rings, double loops, and others. The dipolelayer and the ground plane are each supported by thin planar compositefacesheets; the separation between these facesheets is provided by thincomposite collapsible ‘S’-shaped-springs. The structure is divided intoa number of quartz-epoxy composite strips arranged in concentric squaresand connected to each other using slipping folds. The strips can beflattened, star-folded (folded in the shape of a star), and wrapped topackage within the compact cylindrical volume. A full-scale prototype ofthis reflectarray was constructed and tested. Stowage in the designvolume was successfully demonstrated, and all RF performancerequirements were met, as shown by a pre-stowage RF test and apost-stowage RF test.

Large radio frequency (RF) apertures for small satellites such asCubeSats enhance the capabilities of small spacecraft by enabling higherdata rate telecommunications and higher performance remote sensinginstruments. Since the launch volume of CubeSats is limited, deployableapertures are used. Several deployable RF CubeSat apertures have beendeveloped, to varying levels of technological maturity. Two mechanicaldesign architectures are dominant for deployable RF reflectors for smallsatellites: parabolic mesh antennas (e.g. KaPDA for RainCube, KaTENna),and planar reflectarrays (e.g. ISARA, the MarCO High-Gain Antenna,OMERA, DaHGR). A key example of a CubeSat RF aperture that is not areflector is the S-band 1.24×1.24 m² patch array of antennas developedas described in Ref [1], the disclosure of which is incorporated byreference in its entirety.

The present disclosure describes even larger apertures, to demonstratethe next generation of stowable planar reflectarray technology. Oneembodiment described in the present disclosure is capable of providing a1.5×1.5 m² aperture that can be stowed in a cylindrical volume of 20 cmdiameter and 9 cm height. Therefore, this reflectarray could be stowedin a 4U CubeSat volume. A ‘U’ or a CubeSat unit refers to a cubicalvolume with 10 cm sides. Additional volume will be required for thestowage of associated deployment hardware e.g. booms.

FIGS. 1-2 illustrate an overview of the Large-Area DeployableReflectarray (LADeR) according to one embodiment as described in thepresent disclosure. As visible in FIG. 1, the reflectarray (110) issupported by four deployable booms (115) and connected to the CubeSatbus. A deployable RF feed (105) is attached to the CubeSat bus, as well.FIG. 2 illustrates the CubeSat bus (205) and the four deployable booms(210). The reflectarray is deployed from the bus, and during deploymentthe booms extend the reflectarray to fully extend in the positionillustrated in FIGS. 1-2. FIG. 1 illustrates a top view of thereflectarray, while FIG. 2 illustrates a bottom view.

The present disclosure describes the design of the reflectarraysubsystem. The supporting booms and the deployable feed may be adaptedfrom existing designs known to the person of ordinary skill in the art(e.g. deployable TRAC booms on NanoSail-D). The autonomous andcontrolled deployment of the reflectarray using known deployablemechanisms will also be readily understood by the person of ordinaryskill in the art.

The present disclosure focuses on the innovative RF design for thereflectarray, and on the innovative substrate that supports thereflectarray. The substrate is a collapsible structure that is lighterand more compactable than the solid substrates known to the person ofordinary skill in the art, such as the MarCO high gain antenna (HGA) andISARA. The innovative substrate is also stiffer and capable of a higherdegree of planarity than the creased polymer membrane substratesdescribed for example in Ref [1] and used for DaHGR.

FIG. 3 illustrates an overview of the reflectarray, with zoomed inhighlights of a single strip. The reflectarray comprises multiple stripsin different orientations to form the complete shape. In someembodiments, the reflectarray comprises 4340 cross-dipole elementsspaced 22.5 mm apart in a rectangular lattice that forms a 1.5×1.5 mreflector as illustrated in FIG. 3.

FIG. 3 illustrates multiple strips, such as strip (305), which has awidth of 88 mm. The reflectarray has a 1.5 m edge. A zoomed in view of acorner shows a diagonal cord connection (310), illustrating a diagonalcord (315), a quadrant tension line (320) and a ‘straw’ (325). A zoomedin view of a strip shows a detail of the dipoles shaped like crosses ofdifferent size (330). Another zoomed in detail shows a ligament (335)which joins adjacent strips, comprising a quartz epoxy composite (340)and the ligament proper (345) made of a polyimide film. A side viewshows a cross section of a strip (350), taken across points A-A (360).The cross section shows a plurality of layers (355): dipoles made of 9micrometer thickness copper; a carrier made of 25 micrometers ofpolyimide; a transfer adhesive of 25 micrometers; a facesheet of quartzepoxy of 160 micrometers; an S-shaped spring made of quartz epoxy 80micrometers thick, though in other embodiments the S-springs are 160micrometers thick; a lower facesheet of quartz epoxy of 160 micrometers;a transfer adhesive of 25 micrometers; a carrier of polyimide of 25micrometers; and a ground plane of copper 9 micrometers thick.

The reflector is illuminated by a feed placed at the focal point onemeter above the reflector surface, along the central reflector axis,resulting in an F/D of 0.67. The dipoles lengths are adjusted in orderto change the phase of the reflected signal, thereby collimating theenergy that emanates from the feed. Packaging to fit on a spacecraft asillustrated in FIG. 2 requires a small feed and subreflector assemblymounted to a telescopic waveguide deployment mechanism. However, thepresent disclosure focuses on describing the deployable reflector.Therefore, a small pyramidal horn is used as a stand in for a fulltelescopic waveguide deployable mechanism, with a 10 dB beamwidth ofapproximately 74°. The design of a combined feed and subreflector thatprovides similar illumination and has already been developed asdescribed for example in Ref [2].

The copper cross-dipole elements are photo etched on 25 micrometer thickpolyimide sheets bonded to a quartz epoxy facesheet, an AstroQuartz™(AQ) facesheet, as shown in the cross section (350) of FIG. 3. These AQsheets are supported above a copper ground plane using ‘S’-springs. Thedetails of this construction are described below in the presentdisclosure. An important practical consideration in this design is thatthe fabrication process, in some embodiments, does not providehigh-precision tolerances in several key dimensional parameters.Therefore, in some embodiments, knowledge of the material dielectricconstants may not be highly accurate. To accommodate this, cross-dipoleelements are placed 5 mm above the ground plane. Dielectrics in closecontact with a cross-dipole element have a strong “loading” effect thatwill influence their resonant frequency, but this dielectric loadingeffect decays very rapidly as the dielectric sheets are moved away fromthe dipole. By supporting the dipoles on thin sheets, the dipoles areprimarily influenced by the well-controlled properties of the polyimidelayer, while other dielectrics have less impact. Also, the relativelylarge 5 mm dipole-to-ground plane separation was selected to provide agood range of achievable phase shifts while being relatively insensitiveto dimensional tolerance. Consequently, this arrangement provides arobust, low-mass-density design that minimizes RF dielectric losses.

The reflectarray structure provides two planar parallel surfaces,separated by 5 mm, on which the antenna dipole layer and the groundplane reside. This separation is given by the basic structural unit ofthis reflectarray, which is a strip. As shown in cross section (350), astrip comprises two facesheets separated by a number of collapsible‘S’-shaped springs. Each facesheet is 160 micrometers thick, and is madeof epoxy reinforced with woven quartz fabric. The ‘S’-springs are 160micrometers thick, and also made of the quartz-epoxy composite material.The antenna dipoles and ground plane, each comprising a layer of coppersupported by a carrier layer of polyimide film, are adhered to thequartz-epoxy composite structure using transfer adhesive. In someembodiments the transfer adhesive is not necessary as the polyimidecarrier can be co-cured with the reinforced fabric.

Because of its out-of-plane depth, a strip has substantial out-of-planebending stiffness. This strip bending stiffness contributes to thestiffness of the overall array and is important in maintaining theplanarity of the reflectarray. Additionally, the cross-section of astrip allows it to be flattened elastically for packaging. An ‘S’-springconsists of three flat sections connected by two transversely curvedsections; the two transversely curved sections flex during flattening.The radius of curvature of the transversely curved sections is 5 mm,which ensures that the flattening strain on the ‘S’-springs is less than1.6%, which is within the elastic regime of the strip material. Theflattening strain can be calculated as half the thickness of the‘S’-springs, 160 micrometers, divided by the change in transverseradius, 5 mm.

The strip material, epoxy resin reinforced with woven quartz fibers, waschosen for its dielectric properties, its heritage in space reflectorstructures, its toughness, and its strength. Specifically, Patz™ PMT-F4(a 120° C. cure epoxy resin) and plain weave AstroQuartz™ II 525 wereused. The fiber layups are as follows: two plies arranged in a 0°/90°stack for the facesheets, two plies arranged in a 0°/90° orientation forthe ‘S’-springs; 0° is defined as being along the length of the strip inthis system.

The antenna dipoles and the ground plane consist of a DuPont™ Pyralux™material; this material comprises a layer of 25 micrometers thickpolyimide film clad with a layer of 9 micrometers thick copper. Theantenna dipoles were manufactured by a photolithography process,selectively chemically etching away the copper layer, leaving thedesired arrangement of dipoles intact. The dipole layer and the groundplane were attached to the strip quartz-epoxy substrate using transferadhesive, which was roughly 25 micrometers thick.

As shown in FIG. 3, the strips are arranged in concentric squares. Twodiagonal lines (365) divide the array into four mechanically identicalquadrants. In each quadrant, there are eight strips. Each strip is 88 mmin width; the length of the strip varies from 1.5 m at the outer edge ofthe array to 60 mm at the inner edge near the center. There are 2 mmgaps between the strips, which allow for a structural connection toexist between the strips. This specific arrangement of the strips isdesigned to allow for the stowing of the reflectarray, as furtherexplained below in the present disclosure.

The structural architecture of this reflectarray improves on previousdisclosures as described in Refs. [3,4]. The strips, each of which hasnon-negligible out-of-plane bending stiffness, are “hung” on twopretensioned cords that run along the diagonals of the reflectarray.These diagonal cords are pretensioned by deployable booms as shown inFIG. 2; in the experiments described herein, the booms were substitutedfor a non-deployable cross of PVC tubing. The structural connectionbetween a strip and a diagonal cord consists of a “straw” of fabrictubing that is attached to the end of the strip; the tensioned diagonalcord passes through this “straw”. In a prototype, the diagonal cordswere realized as braided Kevlar™ threads, tensioned by tightening aturnbuckle engaged in series with the cord.

In addition to the diagonal cords, the strips within a quadrant are alsoconnected to each other through slipping folds. This type of fold allowsfor both rotation about and translation along the hinge axis. In thisreflectarray, these slipping folds are realized as a number of ligamentsbetween the strips as illustrated in FIG. 3. To enable creaselessfolding, the Pyralux™ material is mostly cut between the strips; theligaments are lengths of uncut Pyralux™. This allows for the relativefolding and sliding of strips that is required for packaging, butmaintains a degree of structural connectivity between the strips.

From a structural perspective, this reflectarray reacts to in-planeloads through the in-plane tensile and compressive stiffness of thestrips, and the pre-tension in the diagonal cords. Out-of-plane loadsare reacted to by the out-of-plane stiffness of the strips, and thepre-tension in the diagonal cords. Refs. [3,4] describe analytical andnumerical models for predicting the stiffness of such structures. Whendeployed, the structure is sufficiently stiff to maintain its shape in a1 g environment (positioned vertically, so gravity acts in the plane ofthe structure) without any gravity-offloading mechanisms. The mass ofthe prototype reflectarray was measured to be 1.75 kg; this correspondsto an areal density of 0.78 kg/m².

The packaging methodology improves on previous work on slip-wrapping asdescribed in Refs. [3-5]. The strips are connected by slipping hingesthat allow the strips to rotate about and translate along the hingeaxis. This allows the strips to be star-folded, and then wrapped into acompact form, as shown in FIG. 4. In the embodiment of FIG. 4, thestructures use 5 strips per quadrant, but in other embodiments thereflectarray design has a different number of strips per quadrant, suchas 8 strips per quadrant. The general packaging methodology, however, isunchanged: the strips are first flattened and folded into a star-likeconfiguration with 4 arms, and the arms are then wrapped around eachother. The folding of the strips is concurrent with the flattening ofthe strips. This flattening is important, as without it, the stripswould be unable to wrap tightly.

The slipping hinges allow the strips to slip with respect to each otherduring wrapping. This slip is required to accommodate the finite(non-zero) thickness of the flattened strip. By restricting the minimumradius R_(min) during wrapping (and thus the maximum curvature), thestrains during wrapping can be restricted to be within the elastic rangeof the material. Thus the packaging can be an entirely elastic process,with no permanent damage or deformation of the strip structure. Thisallows the reflectarray to return to its original shape afterdeployment.

FIG. 4 illustrates the folding steps (405) and the wrapping steps (410).The strips are flattened into a plane (415), then folded in a star shape(420). The strips can rotate relative to each other thanks to the spaceseparating the strips, and the connections between strips allowing thestrips to rotate relative to the adjacent ones. This allows folding ofthe strips into a tighter star configuration (425) as the surfaces ofadjacent strips are folded against each other. Once the folding has beencompleted (430), a star shape is obtained, comprising 4 arms, each armincluding multiple strips folded together. The arms of the star shapecan then be wrapped in a circular direction, all arms being wrapped inthe same direction, such as clockwise when viewed from the top in FIG. 4(435). When the wrapping is completed (440) a cylindrical compact shapeis obtained. A top view of the cylindrical compact shape (440) is shownin FIG. 5.

FIG. 5 illustrates the predicted wrapped cross-section of thisreflectarray for a minimum wrapping radius of 25.4 mm (505). Given themeasured flattened strip thickness of 610 micrometers, the maximumstrain in the wrapped strips can be estimated as half the thicknessdivided by the radius, which is 1.2%. This value well below thecompressive failure strain of the quartz-epoxy composite material of1.9%. The predicted wrapped form of the reflectarray in FIG. 5 wasgenerated by an algorithm described in Ref [4] that models the wrappedstrips as parallel spiral curves, separated from each other by distancesto account for the non-zero material thickness. The diameter illustratedin FIG. 5 is 200 mm (510).

The quartz-epoxy substrate of each strip was manufactured in 1.5 mlengths in a single-cure process in an oven as described in Ref [15].Plain weave AstroQuartz™ (AQ) II 525 was impregnated with Patz™ PMT-F4epoxy resin at roughly 40% resin content. The AQ prepreg was laid up inthe desired configuration, with five custom-made silicone moldssupporting the AQ prepreg, as shown in FIG. 6. The silicone molds andthe AQ were held in a five-piece aluminum encasement, held together withsteel bolts. This encasement was necessary to constrain thehigh-coefficient-of-thermal-expansion (CTE) silicone molds during the120° C. cure. Also because of this high CTE, the silicone expansionagainst the aluminum encasement provided sufficient pressure to cure theepoxy in the prepreg. As such, even though this process was conducted inan autoclave, the pressurization functionality of the autoclave was notrequired, and the autoclave functioned merely as an oven. In otherembodiments, fabrication activities could be carried out in long ovens,as opposed to autoclaves. FIG. 6 illustrates a cross-section of themolds used to fabricate a strip substrate. FIG. 6 illustrates thealuminum top plate (605), and cage (610) which form the aluminumencasement, as well as the quartz epoxy material (620) which forms theAQ facesheets and the S springs described in FIG. 3, the silicone base(625) and silicone plug (615).

In this embodiment, 20 lengths of strip substrate, each 1.5 m long, weremanufactured. These lengths were then cut into the required shapes,forming the 32 strips of lengths ranging from 0.24 m to 1.50 m. Once cutinto the desired shapes, a layer of Pyralux™ was attached to the bottomfacesheet of the strips using transfer adhesive. This formed the groundplane for each strip. The ground plane is not continuous across allstrips; separate trapezoids of Pyralux™ were attached to the bottomfacesheet of each strip. Pyralux™ AC 092500EV was used for both theground plane and the dipole layer.

To form the dipole layer, eight separate sheets (two sheets perreflectarray quadrant) of Pyralux™ were photolithographically etched. Alaser cutter was also used to cut the sheets to size and to cut theligaments into the material. For each quadrant, the two dipole layersheets of etched and cut Pyralux™ were laid flat on a table, and thestrip substrates were attached to the sheets using transfer adhesive.

The “straws” that connect the ends of the strips to the diagonal cordswere 50 mm long segments of flexible electrical-insulating sleeving madeof woven fiberglass coated with acrylic plastic. These straws were about3.3 mm in outer diameter, and flexible enough to fold and wrap with thestrips. A straw was attached to either end of a strip usingfabric-reinforced adhesive tape. The diagonal cords, made of a braidedKevlar™ thread, were passed through these straws.

For the RF tests, the reflectarray was held in a deployed state using across made of 1-inch-diameter PVC tubing to simulate the four deployablebooms shown in FIG. 2. This cross was then mounted on an aluminumframing. Turnbuckles were used to tension the diagonal cords to anappropriate level, roughly 10 pounds of tension.

The prototype reflectarray was tested for RF performance and forpackaging. The first RF test, RF Test 1, was performed before theprototype was packaged; this test was designed to evaluate the RFperformance of a pristine (i.e. unfolded) reflectarray. Following RFTest 1, the reflectarray was stowed and deployed for Packaging Test 1. Asecond RF test, RF Test 2, was then performed to evaluate changes in RFperformance due to the packaging process. Then, a final packaging test,Packaging Test 2, was performed.

RF Test 1 was conducted using a planar near-field range. The antennaprototype was held vertically, with gravity acting in the plane of thereflectarray. The PVC cross was clamped to a fixture in the range. AnX-band horn, mounted at the focal point of reflectarray, 1 m ahead ofthe dipole layer, was used to illuminate the array for testing. Thefoldable prototype produced a peak of 39.6 dB of gain at 8.4 GHz.

RF Test 2 was conducted after a stow and deploy cycle to determine theeffects of folding and unfolding on the RF performance. This test wasconducted following several months of storage using a vertical planarnear-field range of the same general type as the one used for Test 1.The test setup was comparable to the setup for RF Test 1. The planarranges in both testing facilities used similar hardware.

FIG. 7 shows the frequency-dependent measured gain of the reflectarrayfor both RF tests: test 1 (705) before stowing, and test 2 (710) afterstowing. As can be seen, stowing the reflectarray has very little effecton the gain produced by the antenna; the peak gain dropped by about 0.3dB, and the peak frequency shifted by about 100 MHz. FIGS. 8-9 show themeasured beam patterns from RF Test 2, with FIG. 8 plotting the azimuthvalues for copolarization (805) and crosspolarization (810); and FIG. 9the elevation values for copolarization (905) and crosspolarization(910). As can be seen, the reflectarray produced a well-focused beam inboth azimuth and elevation, with low sidelobe and cross-polarizationlevels.

FIG. 10 illustrates an exemplary packaging sequence for thereflectarray. The deployed reflectarray was placed on a flat steel-toptable 1.5 m in width. The strips were folded manually, following thesequence in panels a)-f). It can be seen how the strips are graduallyfolded from the outside in, for example in panels b) and c). During thisfolding process, the strips were flattened against each other. Bobbypins and large binder clips were used to hold the quadrants and thediagonals folded.

For the second step of wrapping, the star-folded reflectarray in panele) was placed in the middle of four aluminum tubes of known outerradius. The tubes limited the maximum curvature in the wrappedreflectarray. The outer radius of these tubes was 31.75 mm for the firstpackaging test, and 25.4 mm for the second. These four tubes were placeda known distance apart using shoulder bolts inserted in the steel-toptable. The folded reflectarray was then manually wrapped around thesefour tube as seen in panel f). Once fully wrapped, the wrapped array washeld in place by a Velcro™ strap placed around the outer circumferenceof the wrapped structure. FIG. 11 shows a top view of the wrappedreflectarray after packaging.

Once wrapped, the outer circumference of the reflectarray was measuredusing a flexible tape measure. From this, the packaged diameter wasderived to be 241 mm for the first test, and 204 mm for the second test.The packaged height was around the strip width, about 88 mm. Thepackaging efficiency η of the reflectarray can be calculated as thefraction of the cylindrical packaged volume occupied by the material ofreflectarray. This cylindrical packaging volume V_(packaged) was takento have a height of the strip width 88 mm, and the radius as measured.The material volume V_(material) was calculated as the area of thereflectarray A times the measured flattened strip thickness h=610micrometers. The packaging efficiency was calculated to be between 34%and 48%. By refining the packaging process, for example using a jig orautomatic mechanism instead of entirely manual folding, the packagingefficiency can be improved to be higher than 30%, higher than 40% orhigher than 50%.

FIG. 12 illustrates surface flatness measurements for the reflectarray.The surface profile of the reflectarray was measured using a non-contactcoordinate measuring machine (CMM). Specifically, a FARO arm with alaser-line scanner (which provides a measurement accuracy of roughly 50micrometers) was used to scan the entire front surface of the deployedreflectarray. The measured surface RMS was 0.5 mm, much below theλ/20=1.78 mm surface RMS criterion generally applied to RF apertures. Ascan be seen, the bulk of the aplanarity of the array is concentrated onthe outer edges.

The present disclosure described a large-area deployable reflectarrayantenna aperture capable of providing a 1.5 m×1.5 m surface, which canstow in a compact manner in a 6U CubeSat volume. It consists ofbending-stiff strips made of thin composite materials that can beflattened, folded, and wrapped. Since the strips are wrapped withoutpermanent deformation, they can pop-up after deployment to provideseparation between the reflectarray dipoles and the ground plane, andalso provide increased stiffness against bending. The reflectarrayitself consists of an array of crossed-dipoles. The design can also bescaled to larger aperture sizes.

In some embodiment, the plurality of strips comprises four quadrantsforming a square shape, each quadrant having a triangular shapeoccupying a quarter of the square shape, each quadrant comprising aplurality of strips of increasing length arranged to form the triangularshape. In some embodiments, a flatness root means square variation ofthe reflectarray in the deployed configuration is 0.5 mm or less. Insome embodiments, the dipoles and ground plane may be made of aconductive material other than copper; for example, gold or aluminumcould be used. In some embodiments, the dipoles and ground plane are notattached to a carrier, but rather they are attached directly to thefacesheets. In some embodiments, the first facesheet, the secondfacesheet, and the plurality of collapsible S-shaped springs are made ofa material other than an epoxy and woven quartz fabric composite, forexample they are made of a cyanate ester and unidirectional quartzcomposite or other thin, stiff, strong materials. In some embodiments,the ligaments are not made of polyimide, but of other materials such aspolyester or carbon fibers. In some embodiments, the feed is notdeployable.

The examples set forth above are provided to those of ordinary skill inthe art as a complete disclosure and description of how to make and usethe embodiments of the disclosure, and are not intended to limit thescope of what the inventor/inventors regard as their disclosure.

Modifications of the above-described modes for carrying out the methodsand systems herein disclosed that are obvious to persons of skill in theart are intended to be within the scope of the following claims. Allpatents and publications mentioned in the specification are indicativeof the levels of skill of those skilled in the art to which thedisclosure pertains. All references cited in this disclosure areincorporated by reference to the same extent as if each reference hadbeen incorporated by reference in its entirety individually.

It is to be understood that the disclosure is not limited to particularmethods or systems, which can, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification and the appended claims, thesingular forms “a,” “an,” and “the” include plural referents unless thecontent clearly dictates otherwise. The term “plurality” includes two ormore referents unless the content clearly dictates otherwise. Unlessdefined otherwise, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which the disclosure pertains.

The references in the present application, shown in the reference listbelow, are incorporated herein by reference in their entirety.

REFERENCES

-   [1] Warren, P. A., Steinbeck, J. W., Minelli, R. J., and Mueller,    C., “Large, Deployable S-Band Antenna for a 6U Cubesat,” 29th Annual    AIAA/USU Conference on Small Satellites, 2015.-   [2] Chahat, N. E., Hodges, R. E., Sauder, J., Thomson, M., Peral,    E., and Rahmat-Samii, Y., “CubeSat Deployable Ka-Band Mesh Reflector    Antenna Development for Earth Science Missions,” IEEE Transactions    on Antennas and Propagation, Vol. 64, No. 6, 2016, pp. 2083-2093.-   [3] Arya, M., Lee, N., and Pellegrino, S., “Ultralight structures    for space solar power satellites,” 3rd AIAA Spacecraft Structures    Conference, 2016.-   [4] Arya, M., Packaging and Deployment of Large Planar Spacecraft    Structures, Ph.D. thesis, California Institute of Technology, 2016.-   [5] Arya, M., Lee, N., and Pellegrino, S., “Crease-free biaxial    packaging of thick membranes with slipping folds,” International    Journal of Solids and Structures, Vol. 108, 2017, pp. 24-39.-   [6] Schlothauer, A., Royer, F., Pellegrino, S., and Ermanni, P.,    “Flexible Silicone Molds for the Rapid Manufacturing of ultra-thin    Fiber Reinforced Structures,” Society for the Advancement of    Material and Process Engineering (SAMPE 2018), 2018.

What is claimed is:
 1. A deployable reflectarray antenna comprising: aplurality of deployable booms; a radio frequency feed; and areflectarray supported by the plurality of deployable booms andconfigured to: be stored in a folded configuration within a satellitebus, and deploy out of the satellite bus into a deployed configurationduring operation of the satellite, the reflectarray comprising: aplurality of strips, each strip of the plurality of strips comprising: aconductive ground plane; a single first facesheet attached to theconductive ground plane; a single second facesheet; a plurality ofconductive dipoles attached and common to the single second facesheet; aplurality of collapsible S-shaped springs attached to the single firstfacesheet and to the single second facesheet, and being configured to:collapse during folding of the reflectarray, thus allowing the singlefirst facesheet and the single second facesheet to fold against eachother in the folded configuration, and provide mechanical support forthe reflectarray in the deployed configuration by separating the singlefirst facesheet from the single second facesheet, the deployablereflectarray antenna further comprising two diagonally arranged tubulararrangements running along the reflectarray and dividing thereflectarray in four triangularly shaped quadrants, each tubulararrangement being connected to the plurality of strips and comprising aflexible tubing containing a cord pretensioned by the plurality ofbooms, the cord passing through the flexible tubing.
 2. The deployablereflectarray antenna of claim 1, wherein a distance between theconductive ground plane and the plurality of conductive dipoles in thedeployed configuration is 5 mm.
 3. The deployable reflectarray antennaof claim 1, wherein the plurality of conductive dipoles comprisescross-dipole elements having a cross shape.
 4. The deployablereflectarray antenna of claim 1, wherein each collapsible S-shapedspring of the plurality of collapsible S-shaped springs comprises threeflat sections connected by two transversely curved sections, the twotransversely curved sections being configured to flex during folding ofthe reflectarray.
 5. The deployable reflectarray antenna of claim 4,wherein a radius of curvature of the two transversely curved sections inthe deployed configuration is 5 mm, giving a flattening strain for theplurality of collapsible S-shaped springs of less than 1.6%.
 6. Thedeployable reflectarray antenna of claim 1, wherein the single firstfacesheet and the single second facesheet, of each strip of theplurality of strips, have a fiber layup comprising two plies arranged ina 0°/90° stack, wherein 0° is defined as being along a length of eachstrip of the plurality of strips for that respective strip of theplurality of strips.
 7. The deployable reflectarray antenna of claim 1,wherein each collapsible S-shaped spring of the plurality of collapsibleS-shaped springs has a fiber layup comprising two plies arranged in a0°/90° stack, wherein 0° is defined as being along a length of thecollapsible S-shaped spring in the folded configuration.
 8. Thedeployable reflectarray antenna of claim 1, wherein, in the deployedconfiguration, a gap between adjacent strips of the plurality of stripsis 2 mm.
 9. The deployable reflectarray antenna of claim 1, wherein apackaging efficiency of the reflectarray, calculated as a fraction of acylindrical packaged volume occupied by the reflectarray, is greaterthan 30%.
 10. The deployable reflectarray antenna of claim 1, whereineach strip of the plurality of strips has a width of 88 mm.
 11. Thedeployable reflectarray antenna of claim 3, wherein the plurality ofconductive dipoles comprises 4340 cross-dipole elements spaced 22.5 mmapart in a rectangular lattice.
 12. The deployable reflectarray antennaof claim 1, wherein a flatness root mean square variation of thereflectarray in the deployed configuration is 0.5 mm or less.
 13. Thedeployable reflectarray antenna of claim 1, further comprising a firstpolyimide carrier between the conductive ground plane and the singlefirst facesheet, and a second polyimide carrier between the singlesecond facesheet and the plurality of conductive dipoles.
 14. Thedeployable reflectarray antenna of claim 1, wherein the conductiveground plane and the plurality of conductive dipoles are made of amaterial selected from the group consisting of: copper, gold, andaluminum.
 15. The deployable reflectarray antenna of claim 1, whereinthe single first facesheet, the single second facesheet, and theplurality of collapsible S-shaped springs are made of a materialselected from the group consisting of: an epoxy and woven quartz fabriccomposite, and a cyanate ester and unidirectional quartz composite. 16.The deployable reflectarray antenna of claim 1, wherein the tubing ismade of fabric.
 17. The deployable reflectarray antenna of claim 1,further comprising quadrant tensioning lines at ends of said eachtubular arrangement.
 18. The deployable reflectarray antenna of claim 1,further comprising a plurality of ligaments joining adjacent strips ofthe plurality of strips.
 19. The deployable reflectarray antenna ofclaim 18, wherein the plurality of ligaments is made of a materialselected from the group consisting of: polyimide, polyester, and carbonfibers.
 20. A deployable reflectarray antenna comprising: a plurality ofdeployable booms; a radio frequency feed; and a reflectarray supportedby the plurality of deployable booms and configured to: be stored in afolded configuration within a satellite bus, and deploy out of thesatellite bus into a deployed configuration during operation of thesatellite, the reflectarray comprising: a plurality of strips, eachstrip of the plurality of strips comprising: a conductive ground plane;a single first facesheet attached to the conductive ground plane; asingle second facesheet; a plurality of conductive dipoles attached andcommon to the single second facesheet; a plurality of collapsibleS-shaped springs attached to the single first facesheet and to thesingle second facesheet, and being configured to: collapse duringfolding of the reflectarray, thus allowing the single first facesheetand the single second facesheet to fold against each other in the foldedconfiguration, and provide mechanical support for the reflectarray inthe deployed configuration by separating the single first facesheet fromthe single second facesheet.